Circularity of the Replicating Form of a Single-Stranded DNA Virus

Abstract
Electron micrographs of purified replicating form DNA of the bacteriophage øX-174 show that it has ring structure. The circular property may explain both the abnormally high sedimentation coefficient and the great resistance of this DNA to irreversible heat denaturation. Intactness of the circle is required for the control of strand selection during transcription into complementary copies of RNA.